If you are using visual editor then you have to add post excerpt in the excerpt field of post as described in this page http://www.wpbeginner.com/glossary/excerpt/

Also see the following topics regarding answer provided for same question.

https://support.shufflehound.com/forums/topic/change-the-blog-title/#post-2255

https://support.shufflehound.com/forums/topic/excerpt-teammembers-and-timeline-2/#post-3245